Advancing age, as well as injuries, can lead to changes in the various bones, discs, joints and ligaments of the body. In particular, these changes can manifest themselves in the form of damage or degeneration of an intervertebral disc, the result of which is mild to severe chronic back pain. Intervertebral discs serve as “shock” absorbers for the spinal column, absorbing pressure delivered to the spinal column. Additionally, they maintain the proper anatomical separation between two adjacent vertebra. This separation is necessary for allowing both the afferent and efferent nerves to exit and enter, respectively, the spinal column.
Treatment for a diseased or damaged disc can involve the removal of the affected disc and subsequent fusion of the opposing vertebra to one another. Spinal fusion consists of fusing the adjacent vertebrae through the disc space (the space previously occupied by the spinal disc interposed between the adjacent vertebral bodies). Typically, a fusion cage and/or bone graft is placed into the disc space to position the vertebrae apart so as to create more space for the nerves, to restore the angular relationship between the adjacent vertebrae to be fused, and to provide for material that can participate in and promote the fusion process.
More recently, artificial disc replacements have been developed that allow one or more degrees of freedom between the adjacent vertebrae, thereby restoring function to the vertebrae. Surgical procedures for replacing intervertebral disc material, rather than fusing of the vertebrae, have included both anterior approaches and posterior approaches to the spinal column. The anterior approach to the spinal column is complicated by the internal organs that must be bypassed or circumvented to access the vertebrae. The posterior approach (from the back of the patient) encounters the spinous process, superior articular process, and the inferior articular process. These features may be removed to ease insertion of the artificial disc replacement into the intervertebral space, as the disc replacement must have a height sufficient to restore normal height to the adjacent vertebrae, and it must have a depth and width, or surface area, that is sufficient to ensure contact with the peripheral bone, e.g., cortical bone, surrounding the vertebral endplates.
Accordingly, there remains a need for improved methods and devices for replacing a disc.